Because I mix a lot with headphones (which is a very bad idea, but my 9 months old daughter appreciates it ...) and those and my Tannoy Reveals cheat on me when it comes to the frequency spectrum, I use an Analyzer a lot to double-check what I am hearing. My ears tend to get used to too less/ much bass/treble/whatever after listening to a mix a while and the analyzer tells me where I am heading (and should not).
Don't tell anybody, but I once used CurveEQ to match my mix to a commercial recording and let it adjust it automatically... As a nice side effect the matching tells me where I am off.